Generic Audit Trigger CLR C#(Works When The Trigger Is Attached To Any Table)

This Audit Trigger is Generic (i.e. non-"Table Specific") attach it to any tabel and it should work. Be sure and create the 'Audit' table first though.

The following code write audit entries to a Table called
'Audit'
with columns
'ActionType' //varchar
'TableName' //varchar
'PK' //varchar
'FieldName' //varchar
'OldValue' //varchar
'NewValue' //varchar
'ChangeDateTime' //datetime
'ChangeBy' //varchar

using System;
using System.Data;
using System.Data.SqlClient;
using Microsoft.SqlServer.Server;

public partial class Triggers
{
//A Generic Trigger for Insert, Update and Delete Actions on any Table
[Microsoft.SqlServer.Server.SqlTrigger(Name = "AuditTrigger", Event = "FOR INSERT, UPDATE, DELETE")]

public static void AuditTrigger()
{
SqlTriggerContext tcontext = SqlContext.TriggerContext; //Trigger Context
string TName; //Where we store the Altered Table's Name
string User; //Where we will store the Database Username
DataRow iRow; //DataRow to hold the inserted values
DataRow dRow; //DataRow to how the deleted/overwritten values
DataRow aRow; //Audit DataRow to build our Audit entry with
string PKString; //Will temporarily store the Primary Key Column Names and Values here
using (SqlConnection conn = new SqlConnection("context connection=true"))//Our Connection
{
conn.Open();//Open the Connection
//Build the AuditAdapter and Mathcing Table
SqlDataAdapter AuditAdapter = new SqlDataAdapter("SELECT * FROM Audit WHERE 1=0", conn);
DataTable AuditTable = new DataTable();
AuditAdapter.FillSchema(AuditTable, SchemaType.Source);
SqlCommandBuilder AuditCommandBuilder = new SqlCommandBuilder(AuditAdapter);//Populates the Insert command for us
//Get the inserted values
SqlDataAdapter Loader = new SqlDataAdapter("SELECT * from INSERTED", conn);
DataTable inserted = new DataTable();
Loader.Fill(inserted);
//Get the deleted and/or overwritten values
Loader.SelectCommand.CommandText = "SELECT * from DELETED";
DataTable deleted = new DataTable();
Loader.Fill(deleted);
//Retrieve the Name of the Table that currently has a lock from the executing command(i.e. the one that caused this trigger to fire)
SqlCommand cmd = new SqlCommand("SELECT object_name(resource_associated_entity_id) FROM
ys.dm_tran_locks WHERE request_session_id = @@spid and resource_type = 'OBJECT'", conn);
TName = cmd.ExecuteScalar().ToString();
//Retrieve the UserName of the current Database User
SqlCommand curUserCommand = new SqlCommand("SELECT system_user", conn);
User = curUserCommand.ExecuteScalar().ToString();
//Adapted the following command from a T-SQL audit trigger by Nigel Rivett
//http://www.nigelrivett.net/AuditTrailTrigger.html
SqlDataAdapter PKTableAdapter = new SqlDataAdapter(@"SELECT c.COLUMN_NAME
from INFORMATION_SCHEMA.TABLE_CONSTRAINTS pk ,
INFORMATION_SCHEMA.KEY_COLUMN_USAGE c
where pk.TABLE_NAME = '" + TName + @"'
and CONSTRAINT_TYPE = 'PRIMARY KEY'
and c.TABLE_NAME = pk.TABLE_NAME
and c.CONSTRAINT_NAME = pk.CONSTRAINT_NAME", conn);
DataTable PKTable = new DataTable();
PKTableAdapter.Fill(PKTable);

switch (tcontext.TriggerAction)//Switch on the Action occuring on the Table
{
case TriggerAction.Update:
iRow = inserted.Rows[0];//Get the inserted values in row form
dRow = deleted.Rows[0];//Get the overwritten values in row form
PKString = PKStringBuilder(PKTable, iRow);//the the Primary Keys and There values as a string
foreach (DataColumn column in inserted.Columns)//Walk through all possible Table Columns
{
if (!iRow[column.Ordinal].Equals(dRow[column.Ordinal]))//If value changed
{
//Build an Audit Entry
aRow = AuditTable.NewRow();
aRow["ActionType"] = "U";//U for Update
aRow["TableName"] = TName;
aRow["PK"] = PKString;
aRow["FieldName"] = column.ColumnName;
aRow["OldValue"] = dRow[column.Ordinal].ToString();
aRow["NewValue"] = iRow[column.Ordinal].ToString();
aRow["ChangeDateTime"] = DateTime.Now.ToString();
aRow["ChangedBy"] = User;
AuditTable.Rows.InsertAt(aRow, 0);//Insert the entry
}
}
break;
case TriggerAction.Insert:
iRow = inserted.Rows[0];
PKString = PKStringBuilder(PKTable, iRow);
foreach (DataColumn column in inserted.Columns)
{
//Build an Audit Entry
aRow = AuditTable.NewRow();
aRow["ActionType"] = "I";//I for Insert
aRow["TableName"] = TName;
aRow["PK"] = PKString;
aRow["FieldName"] = column.ColumnName;
aRow["OldValue"] = null;
aRow["NewValue"] = iRow[column.Ordinal].ToString();
aRow["ChangeDateTime"] = DateTime.Now.ToString();
aRow["ChangedBy"] = User;
AuditTable.Rows.InsertAt(aRow, 0);//Insert the Entry
}
break;
case TriggerAction.Delete:
dRow = deleted.Rows[0];
PKString = PKStringBuilder(PKTable, dRow);
foreach (DataColumn column in inserted.Columns)
{
//Build and Audit Entry
aRow = AuditTable.NewRow();
aRow["ActionType"] = "D";//D for Delete
aRow["TableName"] = TName;
aRow["PK"] = PKString;
aRow["FieldName"] = column.ColumnName;
aRow["OldValue"] = dRow[column.Ordinal].ToString();
aRow["NewValue"] = null;
aRow["ChangeDateTime"] = DateTime.Now.ToString();
aRow["ChangedBy"] = User;
AuditTable.Rows.InsertAt(aRow, 0);//Insert the Entry
}
break;
default:
//Do Nothing
break;
}
AuditAdapter.Update(AuditTable);//Write all Audit Entries back to AuditTable
conn.Close(); //Close the Connection
}
}


//Helper function that takes a Table of the Primary Key Column Names and the modified rows Values
//and builds a string of the form "<PKColumn1Name=Value1>,PKColumn2Name=Value2>,......"
public static string PKStringBuilder(DataTable primaryKeysTable, DataRow valuesDataRow)
{
string temp = String.Empty;
foreach (DataRow kColumn in primaryKeysTable.Rows)//for all Primary Keys of the Table that is being changed
{
temp = String.Concat(temp, String.Concat("<", kColumn[0].ToString(), "=", valuesDataRow[kColumn[0].ToString)].ToString(), ">,"));
}
return temp;
}
}

The trick was getting the Table Name and the Primary Key Columns.
I hope this code is found useful.

Comments and Suggestion will be much appreciated.